Re: [gplab-users] Ant example in GPLab

[Sara S. <sa...@de...>]

Hi again,

I'm not sure if you are following the latest developments on the 
problem. Here is the MATLAB newsgroup thread link:
http://newsreader.mathworks.com/WebX?14@LK1Ca8Bf0b4@.ef0d8ca

I think there may be a solution in sight... :)

Cheers,
Sara


Sara Silva wrote:

> 
> 
> Aurélien Boffy wrote:
> 
>> ...
>> So, it is us who thank you for your wonderful library and long live 
>> GPLab!
> 
> 
> Well, thank you!
> I am glad GPLAB has been useful to you, not just a source of problems. :)
> 
>> Concerning the problem with the "eval" function:
>>
>> Someone has already replied to your message in the MATLAB newsgroup 
>> and has
>> suggested to pass strings for the function names.
>> We had already tried this idea and that works.
>> ...
> 
> 
> Yes, it works for the artificial ant problem, but it ruins the 
> evaluation of simple symbolic regression problems, or boolean problems, 
> or any other problems that use MATLAB's built-in functions.
> 
> For example:
> s1='plus(plus(2,2),times(3,1))'
> s2='plus(''plus(''2'',''2'')'',''times(''3'',''1'')'')'
> 
> s2 is how s1 would have to be coded if using strings for the function 
> names. While s1 evaluates nicely and fast, without the need to code 
> anything else, s2 requires that plus and times are rewritten and 
> overloaded so they can be evaluated. Otherwise it doesn't work.
> 
>  >> eval(s1)
> ans = 7
> 
>  >> eval(s2)
> ??? Error: ")" expected, "numeric value" found.
> 
> So you understand why this is not a good solution either. The string 
> must be used as it is built, with no further modifications. If that is 
> not possible, I would rather perform the evaluation using the tree 
> instead of the string, as you did. I think it may be possible to use it 
> while avoiding any "hard-coding" of the function names (so that new 
> functions can be added one day without causing problems).
> 
> I am going to try a few other things (I am not expecting any miracle 
> answers from the MATLAB newsgroup) and if I conclude it is not possible 
> to use the string without causing problems, I will code the evaluation 
> using the tree (something using both your code and my code). This way 
> only the ant evaluation will be afected, although I may need to add a 
> few arguments to other related functions.
> 
> Boy, this has made me realize a really important feature of MATLAB that 
> I was totally unaware of!
> 
> Thanks for all your help and suggestions. Do you want to become GPLAB 
> developers? :-)
> 
> Sara
> 
> PS - Sorry to all the mailing list subscribers that are not interested 
> in the artificial ant. But others may be interested in the developments 
> of this problem.
> 
> 
> 
> 
> 
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